I think you're correct but your bar is too high, I think this app would be useful even if it was a lossy approximation Hemingway from his writings. As a thought experiment - I would value what a PhD who dedicated her career to studying one author and their works to tell me what she thinks about a piece of writing from that author's lens. (It's not too far from it)

> Anything else is like trying to eat a picture of a sandwich to satisfy your hunger.

I think it's more akin to you trying to recreate a different sandwich after reading a couple of their cook-books.